That ATR suppression to clinically relevant levels has the potential to be effective in a wide spectrum of cancers is supported by several lines of evidence. Ataxia telengiectasia and rad3-related (ATR) protein kinase is integral to the replication stress response. ATR belongs to a family of kinases, i.e., phosphatidyl inositol 3′ kinase-related kinases (PIKKs), that are involved in the signaling and repair of DNA damage. While other members of this family (ataxia-telangiectasia mutated (ATM) and DNA-dependent protein kinase catalytic subunit (DNA-PKcs)) are required for the repair of double strand breaks (DSBs), ATR is recruited to, and activated by, single strand DNA (ssDNA) generated at stalled replication forks or as an intermediate in the repair of DSBs. Upon replication fork stalling activated ATR phosphorylates the downstream kinase Chk1 resulting in stabilization of the replication fork and inhibition of cell-cycle progression, thus allowing time for resolution of the stress and continued replication. When the ATR-Chk1 pathway is disrupted stalled replication forks collapse into DSBs, thus if unresolved, replication stress can cause genomic instability and negatively impact cell survival (Karlene A. Cimprich & David Cortez, ATR: an essential regulator of genome integrity, Nature Reviews Molecular Cell Biology, August 2008, 9, 616-627). Due to its vital role in replication, loss of ATR is early-embryonic lethal in mice (Eric J. Brown and David Baltimore, ATR disruption leads to chromosomal fragmentation and early embryonic lethality, Genes & Development, 2000, 14, 397-402). However, it is important to note that significant suppression of ATR activity (by more than 90%) by mutations in ATR (as would be replicated by treatment with the inhibitors discussed and disclosed herein) is well tolerated by bone marrow and intestinal epithelium, the tissues that are most sensitive to traditional chemotherapeutics (David W. Schoppy et al., Oncogenic stress sensitizes murine cancers to hypomorphic suppression of ATR, The Journal of Clinical Investigation, 2012, 122(1), 241-252).
ATR inhibition is synthetically lethal in cancers with mutations that cause oncogenic stress or disruption of the DNA damage response (DDR). Genetic changes associated with cancer promote the activation of the replicative stress response and other DNA damage response (DDR) pathways (Di Micco R. et al., Oncogene-induced senescence is a DNA damage response triggered by DNA hyper-replication, Nature 2006 Nov. 30, 444(7119):638-42; Negrini S. et al., Genomic instability—an evolving hallmark of cancer, Nat. Rev. Mol. Cell Biol. 2010 March, 11(3):220-22). Such oncogenic stress inducing alterations include K-RasG12D and H-RasG12V mutations, and c-Myc amplification. Activation of the DDR by oncogenic stress has been proposed to contribute to selection for mutation, and loss of, p53 and ATM (Negrini S. et al., Genomic instability—an evolving hallmark of cancer, Nat. Rev. Mol. Cell Biol. 2010 March, 11(3):220-228). Mutations in the tumor suppressor p53 are found in ˜50% of all human cancers. Similar mutation frequencies are observed in the oncogene Myc, while significant numbers of cancers also harbor mutations in the Ras family of genes (˜16%) and to a lesser degree the DDR protein ATM. Alterations in these genes cause an increased reliance on the ATR-Chk1 pathway for genome maintenance. Studies have found that ATR inhibition elicits synthetic lethality under each of these cancer associated conditions (Gilad O. et al., Combining ATR suppression with oncogenic Ras synergistically increases genomic instability, Cancer Res. 2010, 70(23), 9693-702; Schoppy et. al., J. Clin. Invest, 2012; Reaper P. M. et al., Selective killing of ATM- or p53-deficient cancer cells through inhibition of ATR, Nat. Chem. Biol., 2011, 7(7), 428-30; Menezes D. L. et al., A Synthetic Lethal Screen Reveals Enhanced Sensitivity to ATR Inhibitor Treatment in Mantle Cell Lymphoma with ATM Loss-of-function, Mol. Cancer Res., 2014, Epub ahead of print).
Cancers deficient in components of the homologous recombination pathway, such as those harboring mutations in BRCA1 and BRCA2, are highly sensitive to PARP inhibition (Fong, Inhibition of Poly(ADP-Ribose) Polymerase in Tumors from BRCA Mutation Carriers, New England Journal of Medicine. 2009, 361:123-134). While PARP is required for the repair of single strand breaks (SSBs), preventing their collapse into DSBs, ATR stabilizes replication forks, similarly preventing collapse and formation of DSBs. Loss of PARP and ATR activities therefore both force cells to rely on the DSB repair pathway. It is the inability of BRCA mutant cells to repair DSBs that renders them sensitive to PARP inhibition (Bryant H. E. et al. Specific killing of BRCA2-deficient tumours with inhibitors of poly(ADP-ribose) polymerase, Nature 2005 Apr. 14, 434(7035), 913-7), it is therefore reasonable to suppose that cells deficient in the DDR, such as those harboring BRCA mutations, would also be sensitive to ATR inhibition.
Compounds that inhibit ATR are needed.